The present invention relates to a lubricant composition and a sealed bearing thereof. More particularly, the present invention relates to the lubricant composition which is used by sealing it into a rolling bearing for motors for use in household appliances and apparatuses for industrial use. The rolling bearing is used at high temperatures and rotational speeds and required to have a high degree of quietness, a long life at high temperatures, a low torque, and excellent fretting property. The present invention also relates to the sealed bearing thereof.
The lubricant composition is sealed into the rolling bearing incorporated in apparatuses for industrial use and vehicles to impart lubricant property thereto. The lubricant composition is obtained by kneading a base oil, a thickening agent, and additives used as necessary. As the base oil, mineral oil and synthetic oil such as, ester oil, silicon oil, and ether oil are used. As the thickening agent, metal soap such as lithium soap and urea compounds are used. As the additives, an antioxidant, a rust preventive, a metal deactivator, and a viscosity index improver are added to the base oil as necessary.
In recent years, motor bearings which are used for household appliances and apparatuses for industrial use are rotated at high temperatures and rotational speeds. The motor bearings are demanded to have a high degree of quietness, a high durability at high temperatures and rotational speeds, a low torque, and excellent fretting property.
The lubricant composition containing the base oil including the synthetic hydrocarbon and the ester oil and the urea-containing thickening agent and additives added to the base oil is known (Japanese Patent Application Laid-Open Nos. 9-208982 and 11-270566) as lubricant compositions such as grease excellent in durability at high temperatures, restrained in the generation of noises at low temperatures, and excellent in releasability at a high temperature and a high load.
The grease composition containing the base oil consisting of the ester oil and 3 to 30 wt % of the thickening agent, essentially containing an aliphatic diurea compound, which is added to the base oil is also known as the lubricant composition having a long life in seizing when the rolling bearing is rotated at high temperatures and rotational speeds (Japanese Patent Application Laid-Open No. 2001-107073).
However, these compositions sealed into the bearing do not satisfy all the necessary lubricant characteristics of being excellent in the durability thereof at high temperatures and rotational speeds, excellent in the fretting property thereof, allowing reduction of the torque of the bearing, and allowing the generation of a quiet sound.
The ester oil is preferable as the base oil to improve the durability of the lubricant composition at high temperatures and rotational speeds. The synthetic hydrocarbon oil is preferable to improve the fretting property of the lubricant composition. As the viscosity of the lubricant composition becomes lower, the torque of the bearing decreases but the durability of the lubricant composition at high temperatures and rotational speeds deteriorates. Thus it is very difficult to obtain the lubricant composition satisfying all the above-described necessary characteristics. Therefore the lubricant composition disclosed in Japanese Patent Application Laid-Open No. 9-208982 is insufficient in its durability at high temperatures and rotational speeds. The lubricant composition disclosed in Japanese Patent Application Laid-Open No. 11-270566 causes the rolling bearing to generate big sounds. The grease composition disclosed in Japanese Patent Application Laid-Open No. 2001-107073 is insufficient in its durability at high temperatures and rotational speeds and in its fretting property.